The present invention relates to antennas and, more particularly, to antenna elements transiently formed on a substrate by a light or an electron beam.
Modem communications technology demands the use of antennas operable in many frequency bands with varying gains, polarizations and radiation patterns. The use of radios which can operate over a very broad spectrum of frequencies has heretofore necessitated the use of multiple, narrow frequency band antennas. Because real estate (i.e., the space required to physically implement an antenna) may be limited in some applications, such as aircraft, satellites etc., antennas capable of operating in two or more contiguous or separated frequency bands have been developed. The term xe2x80x9cantennaxe2x80x9d in this description applies to single element antennas as well as antenna arrays which may contain several elements. Antenna elements which operate over a very wide frequency band are well known to those skilled in the antenna art. A spiral antenna is typical of such a wideband antenna element. Such elements may be well suited for a single element application, but they cannot be physically placed in a periodic array configuration without overlapping, whereby the spacing between the centroids of the elements is around xcex/2, where xcex is the wavelength of the highest intended frequency of operation.
In addition, the orientation of conventional antenna elements is predetermined during manufacturing. It is not generally possible to change the orientation of a complex structure such as a spiral antenna from a right-hand circular polarization (RHCP) to a left-hand circular polarization (LHCP) antenna. However, there are some antenna reconfigurations in the prior art used to selectively connect and disconnect antenna components, thereby allowing a physical reconfiguration of the antenna. For example, U.S. Pat. No. 4,728,805 utilizes photonics to combine antenna elements in various forms. The prior art reconfigurable antenna systems suffer from several deficiencies that effect performance and commercialization. For example, if a smoothly curving antenna element, such as a spiral, is required, the edges of the elements remain jagged, affecting the performance of the antenna.
Several other methods are also known to those skilled in the art of antenna design. For example, a technique for putting several individual antenna elements, such as patch antenna elements, in a given area is to overlay or stack them so that the surface of the lower elements behaves as the ground plane for the elements above them. Unfortunately, the higher frequency elements cannot be arrayed close enough to prevent grating lobes when the beam is scanned.
Still another approach is to stack elements made of silicon or other semiconductor material that can become conductive when illuminated with light or electrons. The material is precut into the shape of the antenna element (i.e., dipole, spiral or other shape). In this approach, the array of higher frequency elements is positioned below the low frequency elements to maintain a nearly xcex/4 spacing between the array of elements and the ground plane. When the low frequency elements are in use, the higher frequency elements below them are not illuminated, thereby becoming transparent to RF energy. Similarly, when the high frequency or lower elements are in operation, the lower frequency elements above them are turned off, becoming purely dielectric and transparent. The surface elements, however, never become totally transparent because the semiconductor materials comprise high ∈x dielectric substrates that are not matched to the surrounding composite materials and foams and therefore cause reflections. What is desired is to have the radiators all on one plane.
In U.S. No. Pat. 4,310,843, an electron beam antenna array is depicted, wherein the antenna elements are individually energized by p-n junction devices that are controlled by electron beams from a cathode ray tube device. Although the p-n junctions are within the enclosed structure, the antenna elements connected to the p-n junctions are external to the structure.
Each of the prior art technologies has a limitation in that only preconceived configurations are generally selectable. In other words, even for an antenna system with selectable frequency bands, polarizations, or directional characteristics, only those discrete possibilities designed into the antenna may be selected. The inventive antenna, on the other hand, has no fixed realization, but rather is xe2x80x9cdrawn or paintedxe2x80x9d by an electron beam or the like onto the inner surface of the faceplate. This allows for a great range of possible operations, and simple programming changes applied to the inventive antenna can create a multitude of configurations.
In accordance with the present invention, there is provided a programmable image antenna formed on the face plate of a cathode ray tube. The CRT face is coated with a semiconductor material such as silicon, gallium arsenide, or indium phosphide, instead of the typical phosphors utilized in CRTs for generating a visual image. An electron beam, striking a silicon-coated face plate, creates conductive areas as minority carriers, in the form of electron-hole pairs. The lifetime of the minority carriers may be adjusted by the resistivity of the silicon material. In this manner, antenna elements having a virtually unlimited variety of shapes and/or sizes can be formed on the CRT face. Coupling this technology with MEMS switches or similar technology can produce a reconfigurable antenna system having an unparalleled range of flexibility. RF energy is coupled to the projected elements by means of an RF transmission line and balun connecting directly or capacitively to the computer generated elements or by means of fiber optic lines that connect to optical/RF modulators and demodulators situated behind the screen on which the projected elements are made conductive. In the case of a direct connection, conductive tabs in the form of ohmic contacts are deposited at the feed points in the silicon plate.
Behind the silicon coated screen, inside the cathode ray tube, is a planar grid structure that operates both as a control screen grid for the electronic beams and as the ground plane for the RF elements. More than one grid may be utilized, such as in the form of FSS structures that can act as ground planes situated at xcex/4 at various frequencies.
It is therefore an object of the invention to provide a programmable image antenna system whereby an excitation means such as RF energy or photonics is used to create antenna elements. A further object of the invention is to provide a reconfigurable array antenna system consisting of individually created antenna elements.
Unlike prior art inventions that described reconfigurable antenna elements being formed externally to the system, the antenna elements of the present invention are in an enclosed structure. In addition, the present invention designs the antenna elements directly on the semiconductor material.
It is an additional object of the invention to provide a reconfigurable array antenna system consisting of individually created antenna elements that may be configured as frequency selective surfaces (FSSs) with multiple ground planes.
It is another object of the invention to provide a programmable image antenna system formed on the face of a cathode ray tube (CRT), and wherein the system formed on the face of a CRT can be made selectively absorptive or reflective.
An object of the invention is a programmable image antenna, comprising a substrate adapted for forming an antenna element thereupon, wherein the substrate is in an enclosed structure. There is a coating disposed upon a first surface of the substrate, the coating being conductive in response to impingement of an energy beam that comes from an energy beam source. There is also an energy beam deflection mechanism for deflecting the energy beam in response to externally-generated energy beam deflection signals, thus controlling the beam. Finally, there is a conductive area formed in a selected portion of the coating in response to impingement of the energy beam.
Another object is the programmable image antenna, wherein the substrate comprises the face plate of a cathode ray tube (CRT) and the coating is disposed on the inside of the CRT face plate. In addition, wherein the coating comprises a semiconductor material adapted to release minority carriers comprising electron-hole pairs when impinged by the electron beam, the material comprising one from the group: silicon, gallium arsenide and indium phosphide.
An additional object includes the programmable image antenna, wherein the semiconductor material has a controllable resistivity and the lifetime of the minority carriers is adjusted by controlling the resistivity of the semiconductor material. And, wherein the resistivity is controlled by altering the purity of the semiconductor material.
Yet a further object is the programmable image antenna, wherein the energy beam source comprises one or more electron guns within the CRT and the energy beam comprises an electron beam. The electron guns are configured to work cooperatively to form the antenna elements on the face plate.
Additionally, an object includes the programmable image antenna, further comprising RF energy coupling means operatively connected to the programmable image antenna and adapted for coupling an RF signal to at least one antenna element formed on the CRT face plate. The RF energy coupling means comprises at least one from the group: transmission line and balun. And, the RF coupling means further comprising direct connection conductive tabs deposited at predetermined points on the CRT face plate, wherein the conductive tabs comprise aluminum contacts and the predetermined points comprise feed points, the contacts being plated at the feed points on the coating on the face plate of the CRT.
And a further object is for the programmable image antenna further comprising at least one substantially planar grid structure disposed within the CRT intermediate the electron gun and the face plate. Including at least one of the at least one substantially planar grid structures is configured to serve as a ground plane. Also, the programmable image antenna with at least one planar grid structure disposed approximately in a xcex/4 relationship relative to the face plate at a predetermined operating frequency. Finally, the programmable image antenna, wherein the at least one substantially planar grid structures comprises at least two planar grid structures disposed within the CRT intermediate the electron gun and the CRT face plate, the at least two planar grid structures being configured to form a frequency selective surface.
Yet an additional object is the programmable image antenna, wherein the antenna elements are formed on the substrate in at least one pattern from the group: right-hand spiral, left-hand spiral, bow-tie, horizontally-polarized dipole, vertically-polarized dipole.
An object includes the programmable image antenna wherein the energy beam deflection system comprises a cursor addressable energy beam control system.
An object also includes the programmable image antenna, wherein the antenna elements are maintained on the CRT face by substantially continuously refreshing the conductive areas by the energy beam and the energy beam deflection mechanism.
An object of the invention is a programmable image antenna, comprising a substrate adapted for forming an antenna element thereupon, wherein the substrate is in an enclosed structure. There is a coating disposed upon a first surface of the substrate, the coating being conductive in response to impingement of an energy beam. There is an energy beam source for generating the energy beams, and an energy beam connection mechanism for delivering the energy beam, whereby a conductive area is formed in a selected portion of the coating in response to impingement of the energy beam.
In this embodiment an object is for a programmable image antenna wherein the substrate comprises the face plate of a cathode ray tube (CRT) and the coating is disposed on the inside of the CRT face plate. An object for this embodiment is the programmable image wherein the energy beam source is photonic. In addition, wherein the energy beam connection mechanism is fiber optic. Finally, an object is the programmable image antenna, wherein the coating comprises a photonically activated coating.